A mechanical spline is commonly used to couple a shaft and collar to transmit rotational motion and torque. If no adjacent feature such as a shoulder on the shaft or a counter bore on the collar exists, the full length of spline is engaged and can be utilized for strength and traditional manufacturing methods can be used to produce each component. However, if one or both members have adjacent features, a spline relief is required to allow for tool clearance. The length (or width) of the annular relief(s) reduce(s) the full length of spline engagement which reduces the strength of the connection proportionally. Common prior art methods of machining splines close to adjacent features include shaping and milling. Shaping involves a fixed cutting tool parallel to the spline axis, moving through the usable portion of the spline, into the annularly shaped relived area, and stopping short of the adjacent feature before retracting, reversing direction, and repeating the cycle. Milling involves a rotating cutting tool normal to the spline axis, moving through the usable portion of the spline, into the annularly shaped relived area, and stopping short of the adjacent feature before retracting, reversing direction, and repeating the cycle.
FIG. 1 is a cross-sectional diagrammatic view 100 taken along the lines 1-1 of FIG. 1A of the prior art external spline illustrating the workpiece 101A having a base 101, shoulder 102, cylindrical external spline portion 199, and annular tool relief 103 together with a traditional cutter-shaper 106 and its operating path 108. The cylindrical external spline includes a plurality of teeth 104. Reference numeral 105 indicates the top end portion of the spline.
Still referring to FIG. 1, the cutter-shaper tool 106 includes a plurality of cutter-shaper tool blades 107 which cut the workpiece 101A, or more particularly, which cut the cylindrical spline portion 199. Cutter motion 108 includes a downward stroke 109 of cutter-shaper 106, then a lateral or transverse stroke 110 removing the cutter-shaper tool 106 from the spline (workpiece), then a longitudinal or upward stroke 111 of the cutter-shaper tool, and finally a repositioning stroke 112 moving the cutter-shaper tool 106 in alignment for another cut. Several or multiple passes of the cutter-shaper tool are made to produce a finished part. The workpiece 101A is simultaneously rotated with the cutter shaper tool 106.
FIG. 1A is a perspective view 100A of FIG. 1 and illustrates the annular cutter-shaper tool relief 103 extending circumferentially around the upper cylindrical portion bearing the external spline and underneath the external spline teeth. Referring to FIG. 1A, tooth 121, side of tooth 122 and tooth fillet 123 are illustrated. FIG. 1B is an elevation view 100B of prior art FIG. 1A. FIG. 1C is a top view 100C of prior art FIG. 1A illustrating the same components described above.
FIG. 2 is a perspective view 200 illustrating the base 201, counterbore engagement surface 206, cylindrical internal spline portion (tooth 205, tooth space 204), and shaper-cutter tool relief 203 of the female connection member (collar member) 201A. Reference numeral 202 is used to denote the top of the female connection member 201A. Reference numeral 220A denotes the internal spline. Not shown is the prior art cutter-shaper tool which makes the female collar connection.
FIG. 2A is a cross-sectional view 200A of prior art taken along the lines 2A-2A of FIG. 2. Inner circumferential shaper-cutter tool annular tool relief 203 is illustrated well in FIG. 2A as is counterbore engagement surface 206. Representative tooth 205 and representative tooth space 204 are illustrated well in FIGS. 2A and 2B. FIG. 2B is a top view 200B of FIG. 2.
FIG. 3 is a cross-sectional schematic view 300 of a prior art internal spline 220A and a prior art external spline 199 coupled together illustrating the effective face width, EF, annular cutter-shaper tool reliefs 103, 203 and the total length of the spline connection, SC. EF, the effective face width, of the prior art spline connection is relatively short and thus the length limits the load. By relatively short, it is meant that the effective face width, EF, is just a portion of the spline connection length. The EF of the prior art spline connections may be only 50% of the length of the spline connections. As illustrated in FIG. 3, the manufactured face width, FW, of the exterior spline 199 and the interior spline 220A, are equal.
In designing a spline, the load (torque) required to be transmitted by the spline connection is identified. Next, the spline size as a function of torque required determines an approximate range of the necessary pitch diameter. The torque carrying capacity of a spline is a function the pitch diameter, the shear stress and the length of the spline connection, SC. Once the pitch diameter is specified, the design engineer then calculates the length of the spline connection taking into account that all teeth of the inner and external spline teeth may not be in engagement. It is important to efficiently use the spline connection and to maximize the effective face width, EF in order to transmit torque efficiently. In the prior art illustrated in FIGS. 1, 1A, 1B, 1C, 2, 2A, 2B, and 3, a large annular cutter-shaper relief is required between the end of the spline and an adjacent feature to allow the cutter-shaper to fully cut and retract from the spline. The annular cutter-shaper relief is designated as CR on FIG. 3 and the effective face width is expressed as follows:EF=SC−2CR
Therefore, it can be readily seen from FIG. 3 that length of the annular cutter-shaper tool reliefs reduce the effective face width of the prior art spline connection. The problem with annular cutter-shaper tool reliefs occurs whenever splines are manufactured adjacent features. Typically, the adjacent features are shoulders and counterbores but any adjacent feature regardless of the name applied to it will cause a problem as it will require a substantial tool relief.